1. Field of the Invention
This invention relates to conversion of heavy hydrocarbon oils into more valuable products, and more particularly relates to conversion of heavy hydrocarbon oils by an improved hydrogen donor diluent cracking process.
2. The Prior Art
Hydrogen donor diluent cracking (HDDC) of heavy hydrocarbon oils has been known for many years as a possible approach to upgrading of heavy hydrocarbon oils.
U.S. Pat. Nos. 2,873,245 and 2,953,513 both describe the HDDC process, and disclose wide ranges of potential operating conditions.
Canadian Pat. No. 555,631 describes use of hydrogen donor diluent in recovering oil from shale and tar sands.
Numerous other patents and literature references are directed to variations of HDDC. However, the HDDC process has not been widely utilized, partly due to the high capital costs associated with the high pressure equipment normally considered necessary for a commercial version of the HDDC process.
It is generally known that HDDC processes are more effective at higher temperatures, and that conversion yields are a function of reaction time. However, conversion at low temperature and long residence time can only be enhanced by increasing the system pressure with resultant high capital costs, while conversion at low pressure and high temperature is limited by unwanted formation of coke.
Prior to this invention, it has been generally believed that the HDDC process had to be carried out at low temperature (less than about 875.degree. F.) and/or high pressure (greater than 1,000 psig). This belief probably resulted from the fact that exploratory work in this area was conducted in autoclaves, and the long heat up and cool down periods for autoclave work imposed a minimum on the reaction times that could be investigated. Long residence times lead to coke formation as the reaction temperature is increased.
It is an object of this invention to provide an HDDC process which does not require long residence times or high pressure, and which avoids the formation of coke.
It is a further object to provide an HDDC process which utilizes high temperature and short residence time at moderate pressure to provide high conversion yields without coke formation.